Vehicles known from the practice are designed for maneuvering with at least one steerable axle constructed in a manner on the driving system of the vehicle and on the type of wheel suspension. The driver's steering movements or a steering demand are basically transmitted to the wheels of the steerable axle of the vehicle via a steering wheel, a steering column, a steering gear and a swinging kinematics consisting of several parts interconnected by joints so that the wheels of the steerable vehicle axle are designed, swingable from a position equivalent to a straight-ahead start.
In the construction of the vehicle, a fundamental differentiation must further be made between a so-called rotary steering system and a so-called knuckle steering system. That is, the wheels of a steerable vehicle axle having wheels adjusted according to a required steering angle in conformity with the principle of rotary steering, together with an axle extending between the wheels in transverse direction of the vehicle, are swung around a common pivot or around a common steering axis of rotation; a base of the vehicle being reduced by the swinging of the axle and of the wheels whereby a rocking inclination of the vehicle increases. The rotary steering is preferably used in two-axle trailers, since a vehicle designed with a rotary steering system stands out by good maneuverability.
If the steering motions demanded are converted, according to the knuckle steering system principle, each wheel of the steerable vehicle axle is swung around its own steering axis of rotation located on the ends facing the wheels of an axle extending in a transverse direction of the vehicle between the wheels of the steerable vehicle axle. The steering axes of rotation are formed by the connections of the steering points of the wheel suspension or by the longitudinal axes of the knuckle pins. The knuckle steering principle is preferably used in double-tracked motor vehicles, since the base of the vehicle remains at an almost equal dimension when the turn wheels around the coordinated steering axes of rotation whereby a rocking inclination of the vehicle increases to a substantially lesser extent than when using a rotary steering system.
The higher the demands on the maneuverability of a vehicle, increase in the maximum swinging angle of the axle in a rotary steering system or the steering angle of the wheels around the steering axes of rotation in a knuckle steering system are to be provided. Especially in construction machines, a turning circle is required to be as small as possible since, as is common in the use of construction machines, the space available for maneuvering is extensively limited and expensive driving maneuvers are uneconomic.
As a rule, the steering systems of construction machines, especially of telescopic loaders, are designed as knuckle steering systems where the steering movements of a driver are applied to the wheels via a main steering cylinder designed as a synchronous cylinder with continuous piston rod. The power between the wheels and the piston rod of the main steering cylinder is transmitted via a track rod which, in turn, is connected with a joint housing or a wheel head operatively connected with one wheel and jointly is swung around the coordinated steering axis of rotation.
If both swingable wheels of a vehicle, steerable with a knuckle steering system, are equally strongly turned, neither of the two wheels can roll on its natural path. Each wheel is then forced by the other wheel to an unnatural path so that both wheels, in addition to the rolling motion, also perform a more or less strong sliding motion upon the foundation which results in undesired wear of the wheels.
For this reason, basically in the operation of a vehicle and particularly when cornering, the wheels must roll without lateral sliding movement which, under certain circumstances, is very cumbersome for the tires as is the case in a rotary steering system. In knuckle steering systems, this is accomplished by the steering angle of the wheel inside the curve being larger than that of the wheel outside the curve.
The problem of the high tire load during cornering additionally occurs not only between the wheels of a vehicle axle. According to the so-called Ackermann principle, the extended center lines of the knuckle of the turned wheels, for an operation of the vehicle with as little wear as possible or no wear at all, have to strike upon the extended center line of a second non-steerable vehicle axle or intersect at precisely one point with the extended central lines of the knuckles of the wheels of a second steerable vehicle axle. The orbit traversed by the wheels of the two vehicle axles then have a common central point so that the above described sliding motions of the wheels are considerably reduced or entirely prevented.
If the lines or extensions of the center lines of the knuckles of the wheels do not strike at one point, there exists a so-called track angle error or a so-called steering angle error.
In construction vehicles which are designed with short wheel bases, the same as with steerable axles according to the knuckle steering principle in the area of the front axle and also in the area of the rear axle, the Ackermann geometry results which constitutes the ideal ratio between the steering angle position of the wheel inside the curve and the steering angle position of the wheel outside the curve from the half wheel base, wherefore the optimal steering angle position of the wheel outside the curve to the steering angle position of the wheel inside the curve is relatively small. However, determined by the principle of steering kinematics used in the practice, there disadvantageously appears an undesirably great divergence from the optimal steering angle of the wheels, since the steering angle position of the short outer wheel relative to the steering angle position of the wheel inside the curve is too large and besides the inclines transit angle of the tires increases sharply as the steering angle increases. From the above mentioned great divergences from the optimal steering angle and the sharply increasing inclined transit angle of the tires, an undesirable great wear of the tires results when cornering and, in addition, stresses generate in the drive train which require larger dimensions of the parts of the drive train whereby both the operation costs and the production costs of construction vehicles are disadvantageously increased.
Therefore, the problem on which this invention is based is making a vehicle available which stands out, on one hand, by great maneuverability and, on the other hand, both by small tire load and by small stresses in the drive train when cornering.